This invention is in the field of integrated circuits and in the field of marking integrated circuits for tracking purposes.
There is a need in the semiconductor industry for a reliable method of marking integrated circuit die (“chips”) to facilitate tracking of these devices after they are manufactured and sent to customers worldwide. For example, in instances where a customer detects an imperfection in a particular chip, or desires more chips that behave like a particular chip, the ability to ascertain the provenance of the chip and the conditions under which it was fabricated can constitute a competitive advantage for an integrated circuit manufacturer. Whereas, in the past, the marking of the chips on a particular wafer has been possible, it has been possible to only mark chips with a gross level of identification, since all of the chips on a wafer in a given lot of wafers of a particular type of integrated circuit are made with the same set of reticles or masks. Since, for a given level in the fabrication of the chip, that same reticle is stepped across the entire wafer, it has not been possible to give each individual chip its own identifying mark during the wafer fabrication process, where it is most cost efficient to do so. Thus, a problem with a particular chip can only also be traced back as far as the level of identification on the chip allows.
In addition, the continuing demand for smaller chips has put space at a premium and has complicated the task of marking. Typically, all of the wafers in a lot bear the same mark, indicating the device design type, year and month of manufacture, and perhaps the location of manufacture. The identifying mark is also typically large enough to be visually identified with a microscope, for example. As the demand for smaller chips is increasing, the space available for placing such information on each chip has diminished accordingly. For example, for a 1.5 mm×1.5 mm device package, it is not unusual to have space sufficient on the chip for only about five identifying characters, three for the device type and two for the year and month of manufacture, for example. A defect in such a device can only be traced to the year and month in which the chip was made. In many cases, a manufacturer may have fabrication facilities all over the world and many thousands of wafers produced by each of those facilities a month, so much more detailed marking of such small chips is needed. It is clear that there is a need in the industry for better ways of marking integrated circuit die.